Family B DNA polymerases from archaea, such as Pyrococcus furiosus (Pfli-Pol), stall replication upon encountering template strand uracil and hypoxanthine (the deamination products of cytosine and adenine spectively) four base pairs ahead of the primer template junction. The deaminated bases bind to a specialized pocket within the amino terminal domain of the polymerase. This read-ahead mechanism could be a final attempt to detect deaminated bases and repair them by an as yet undetermined pathway, preventing 50% of the progeny inheriting a transition mutation.